CBSE Class 8

On this page, you will find Combustion and Flame Class 8 Notes Science Chapter 6 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 6 Combustion and Flame will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 6 Combustion and Flame

Combustion and Flame Class 8 Notes Understanding the Lesson

1. Combustion is a chemical process in which a substance reacts with oxygen to give out heat energy.

2. All the substances that undergo combustion are said to be combustible.

3. A combustible substance may be solid, liquid or gaseous.

4. The presence of air is very necessary for combustion.

5. The lowest temperature at which a substance catches fire is known as its ignition temperature.

6. Some substances have very low ignition temperatures and they catch fire easily with a flame. They are known as inflammable substances; e.g., Petrol, LPG (Liquefied Petroleum Gas), alcohol, etc.

7. There are three significant requirements for producing fire fuel, air (for the supply of oxygen), and heat (to raise the temperature of the fuel above its ignition temperature).

8. When a substance burns rapidly and produces heat and light, the combustion is called rapid combustion.

9. When a material begins to burn suddenly without any external supply of heat or friction, the combustion is called spontaneous combustion; e.g., white phosphorus catches fire even at 25°C.

10. So, when the temperature goes beyond 25°C in summer, it catches fire automatically.

11. During combustion, when a large amount of heat and light is released with a bang or force, along with the production of gas, the combustion is called an explosion; e.g., bombs and fireworks, etc.

12. Flame is the region where combustion of gaseous substances or vapour goes on.

13. There are three distinct zones of a flame dark zone, luminous zone and non- luminous zone.

14. The amount of heat energy produced on burning 1 kg of a fuel completely is called the calorific value of that fuel.

15. The calorific value of a fuel is expressed in a unit called kilojoule per kilogram (kJ/kg).

16. A good fuel is one which is readily available, cheap, burns easily, produces large amount of heat and does not leave any undesirable substances.

17. The cutting down of trees is termed as ‘deforestation’.

18. The rise in temperature of the atmosphere of the earth is called global warming.

19. Water is commonly used to extinguish fire.

20. Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain.

Class 8 Science Chapter 6 Notes Important Terms

Acid rain: Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain. It harms trees, crops and buildings.

Calorific value: The amount of heat energy produced on combustion of 1 kg of fuel completely is called its calorific value.

Combustion: It is a chemical process in which a substance reacts with oxygen (in air) to emit heat and light.

Deforestation: The removal of trees on a large scale is termed as deforestation.

Explosion: A combustion reaction during which a large amount of heat and light energy is released, along with a bang or force with the production of gas, is called explosion.

Flame: It is a region where the combustion of gaseous substances or vapour goes on.

Fire extinguisher: A manually operated device used for extinguishing fire is known as a fire extinguisher.

Fuel: It is a material which is burn to produce heat.

Fuel efficiency: It is a parameter used to check the quality of fuel. It is expressed in term of its calorific value.

Global warming: An increase in the average temperature of the earth’s atmosphere, especially a sus-tained increase that causes climatic changes.

Ideal fuel: It is the fuel, that satisfies all the necessities of a fuel for specific uses.

Ignition temperature: The lowest temperature at which a substance catches fire is called its ignition temperature.

Inflammable substances: They are the substances that have a very low ignition temperature, and that can easily burn with a flame.

On this page, you will find Coal and Petroleum Class 8 Notes Science Chapter 5 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 5 Coal and Petroleum will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 5 Coal and Petroleum

Coal and Petroleum Class 8 Notes Understanding the Lesson

1. All the things that are required to fulfil our needs are called resources.

2. Some resources like air, water, fuels, plants occur in nature. They are called natural resources.

3. Some resources like plastics, machines, etc., are man-made.

4. Natural resources are classified as:

• Inexhaustible natural resources and
• Exhaustible natural resources.

5. Inexhaustible natural resources are present in unlimited quantity in nature; e.g., sunlight, air, etc. Exhaustible natural resources are present in limited quantity in nature; e.g., petroleum, natural gas, wildlife, forest, etc.

6. Some of exhaustible resources are renewable while some are non-renewable.

7. Natural fuels that are made up by the dead remains of living organisms for over a long period of time, are called fossil fuels.

8. Fossil fuels may be divided into three categories:

• Solid – Coal
• Liquid – Petroleum
• Gas – Natural gas

9. Coal is black-coloured hard substance that mainly contains carbon.

10. Coal is one of the main sources of energy worldwide.

11. Coal is one of the fuels used to cook food, run engines, generate electricity and to run various industries. Millions of years ago, trees, plants, ferns and forests got buried below the rocks, soil and sand.

12. Under anaerobic condition high temperature and pressure, the carbon enriched organic matter of plants slowly got converted into coal.

13. This slow process of conversion of wood into coal is called carbonisation.

14. Destructive distillation of coal is done at 1000°C in absence of air to obtain many other useful organic and inorganic substances from it, such as coke, coal tar and coal gas.

15. Coke is a tough, porous and black substance. It is an almost pure form of carbon.

16. Coke is used in the manufacture of steel and in the extraction of many metals.

17. Coal tar is a black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances.

18. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and industry like dyes, drugs, naphthalene balls, paints, plastics, etc.

19. Coal gas is produced during the processing of coal to get coke.

20. It is used as a fuel in many industries situated near the coal processing units.

21. The word ‘petroleum’ is derived from petra meaning ‘rock’ and oleum meaning ‘oil’.

22. Petroleum is a dark coloured viscous fluid and like all the other oils, it is lighter than water.

23. Petroleum was formed when organisms living in the sea are buried underneath sedimentary rock and subjected to intense heat and pressure under anaerobic condition.

24. Petroleum has such a great significance that it is named as ‘black gold’.

25. Separation of different constituents of petroleum through fractional distillation is called refining of petroleum.

26. Refining of petroleum is carried out in a petroleum refinery.

27. Natural gas is a very important fossil fuel because it is easy to transport through pipes.

28. Natural gas is stored under high pressure as compressed natural gas (CNG).

29. The great .advantage of CNG is that it can be used directly for burning in homes and factories.

30. We must use the fuels only when it is absolutely necessary.

31. In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/ diesel while driving.

32. To conclude, we can say that fossil fuels are our very important resources of energy. But as they are limited, we should use them judiciously.

Class 8 Science Chapter 5 Notes Important Terms

Coal: A fossil fuel, formed by the decay of vegetation which existed millions of years ago is called coal.

Coal gas: A mixture of gases produced during destructive distillation of coal is called coal gas.

Coal tar: Coal tar is a black coloured thick, viscous liquid which is obtained as byproduct when coal is carbonised to make coke.

Coke: On heating the coal strongly, the volatile impurities escape out from it and solid, pure carbon residue is left behind which is called coke.

Fossil fuel: Natural fuel that made up by burial of living organisms under deep down the earth for over a long period of time is called fossil fuel.

Natural gas: The gaseous mixture of lower hydrocarbon which occur deep inside the earth either alone or covering the crude oil in an oil field is called natural gas.

Petroleum: A dark coloured thick crude oil found deep below the ground is called petroleum.

Petroleum refinery: A place where process of separating the various constituents of petroleum is car-ried out is called petroleum refinery.

On this page, you will find Materials: Metals and Non-Metals Class 8 Notes Science Chapter 4 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 4 Materials: Metals and Non-Metals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 4 Materials: Metals and Non-Metals

Materials: Metals and Non-Metals Class 8 Notes Understanding the Lesson

1. Materials can be broadly grouped into two groups metals and non-metals.

2. Substances which are generally hard, lustrous, malleable, sonorous and good conductors of heat and electricity are metals. For example, copper, iron, gold, silver, etc.

3. Substances which are generally soft, dull in appearance, brittle, non-sonorous and bad conductors of heat and electricity are non-metals. For example, oxygen, hydrogen, carbon, sulphur, etc.

4. The property of metals by which they can be beaten into thin sheets is called malleability.

5. The property of metal by which it can be drawn into wires is called ductility.

6. The property of metal of producing ringing sound is called sonority.

7. Chemical properties of metals and non-metals:

(i) Reaction with oxygen: Both metals and non-metals form their oxides when burnt in oxygen. Metals form basic oxides whereas non-metals generally form acidic oxides.
Reactions of metal or non-metal with oxygen are called oxidation reactions.

(ii) Reaction with water: Metals produce their oxides or hydroxides and hydrogen gas on reacting with water. Non-metals do not react with water.

(iii) Reaction with acids: Metals react with acids and produce metal salts and hydrogen gas. Hydrogen gas burns with a ‘pop’ sound, when a burning matchstick is brought near it.
Non-metals generally do not react with acids.

(iv) Reaction with bases: Most of the metals and non-metals generally do not react with bases. Some metals like aluminium, lead and zinc react with strong bases like sodium hydroxide to make complex salts and hydrogen gas. Similarly, sometimes some complex reactions take place between non-metals and bases.

(v) Displacement reactions: Reactions in which more reactive metal displaces the less reactive metal from its salt is called displacement reactions. Certain metals are capable of displacing other metals from their solutions. For example, zinc (Zn) replaces copper from copper sulphate solution. The reaction is as follows:

8. On the basis of reactivity of metals a sequence is formed called reactivity series. Metals on the top of the series are most reactive and those on the bottom are least reactive. Zinc is more reactive than copper and iron. A more reactive metal can replace a less reactive metal but, a less reactive metal cannot replace a more reactive metal.

9. Uses of metals: Metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, water boilers, utensils, etc. They are also used in making wires and sheets.

10. Uses of non-metals

• All living beings inhale oxygen during breathing, which is a non-metal.
• Non-metals like nitrogen, phosphorus and potassium are used in fertilisers to enhance the growth of plants.
• Non-metal like chlorine is used in water purification process.
• Non-metal is used in the purple coloured solution which is applied on wounds as an antiseptic.
• Non-metals are used in crackers.

Class 8 Science Chapter 4 Notes Important Terms

Atom: An atom is the smallest particle of an element which cannot be further divided by any physical mean.

Conductor: Substance which allow heat and electricity to pass through it is called conductor.

Displacement reaction: Reaction in which more reactive element displaces less reactive element is known as displacement reaction.

Ductility: The property of metals due to which they can be drawn into wires is called ductility. Metals are ductile.

Elements: The substances whose molecules are made up of only one type of atoms are known as elements.

Hardness: It is the property of a substance due to which it cannot be cut easily is called its hardness. Metals possess this property.

Malleability: It is the property of a substance due to which it can be beaten into thin sheets is called malleability. Metals have this property.

Metals: Substances which are generally shiny, hard, malleable, ductile, sonorous and good conductors of heat and electricity are metals.

Metalloid: Substances which possess properties of both metals and non-metals are called metalloids. For example, bismuth, antimony, arsenic and boron.

Non-metals: Materials which are soft, dull in appearance, non-sonorous and poor conductors of heat and electricity are called non-metals. They break down into a powdery mass on tapping with a hammer. They also form negative ions by gaining electrons.

Sonorous: The property due to which metals produce a ringing sound is called sonority. This is why metals are called to be sonorous.

On this page, you will find Synthetic Fibres and Plastics Class 8 Notes Science Chapter 3 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 3 Synthetic Fibres and Plastics will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 3 Synthetic Fibres and Plastics

Synthetic Fibres and Plastics Class 8 Notes Understanding the Lesson

1. A fabric is the material used for making clothes.

2. Fabrics are made from fibres obtained from natural or artificial source.

3. Beside clothes, fibres are also used for making carpets, sail of boats, parachutes, upholstery and many more items.

4. Fibres can be natural or artificial. Fibres such as cotton, wool, jute and silk are natural fibres whereas rayon, nylon and polyester are artificial fibres.

5. The man-made fibres produced from chemical substances are called synthetic fibres.

6. Synthetic fibres are also known as man-made fibres or artificial fibres.

7. Depending upon the types of chemicals used for manufacturing of the synthetic fibres they are called rayon, nylon, polyester and acrylic.

8. Rayon or artificial silk is made from cellulose obtained from wood pulp.

9. It can be dyed in a wide variety of colours.

10. Nylon was the first synthetic fibre produced by man in 1935.

11. Nylon fibres are strong, elastic, light, lustrous and easy to wash.

12. It is used to make many items like socks, ropes, tents, toothbrushes, car seat belts, curtains, etc.

13. Terylene and dacron are polyester fibres.

14. It is made from two monomers, terephthalic acid and ethylene glycol.

15. It is used for making PET bottles, jars, floppy discs, shirts, hats, etc.

16. Acrylic is the synthetic fibre that resembles wool in its texture and properties.

17. It is used to make sweaters, shawls, socks, etc.

18. They dry up soon, are durable, less expensive, readily available and easy to maintain.

19. A plastic is a synthetic material which can be set into desired shape when soft and then hardened to produce a durable article.

20. Some plastic polymers have linear arrangement of units, whereas in others it is cross-linked arrangement.

21. Thermoplastic is a plastic which gets deformed easily on heating and can be bent easily, e.g., polythene and PVC. These are used for manufacturing toys, combs, containers, etc.

22. Thermosetting plastics is a plastic which when moulded once cannot be softened by heating, e.g., bakelite and melamine.

23. Bakelite is used for making electrical switches, handles of various utensils, etc.

24. Melamine is used for making floor tiles, kitchenware, etc.

25. Plastic is a non-biodegradable substance. So, the articles made of plastics do not rot when they are thrown away after use. This pollute the environment.

26. When the plastic waste materials are burnt, they produce poisonous gases which pollute the air. The 4R principle, Reduce, Reuse, Recycle and Recover should be our basic mantra to minimise the hazards associated with the disposal of plastic wastes.

27. We must think twice before using plastic items.

Class 8 Science Chapter 3 Notes Important Terms

Acrylic: The synthetic fibre that resembles wool in its texture and properties is called acrylic.

Artificial silk: A man-made fibre obtained from chemical treatment of wood pulp which has properties similar to that of silk is called artificial silk.

Nylon: A fully synthetic polymer which is prepared from coal, water and air is called nylon.

Plastic: Those substances which are mostly synthetic in nature, obtained mainly from petrochemical sources and can be moulded into different shapes are called plastics.

Polyester: The synthetic fibre which is used for making PET bottles, home furnishings, etc., and are blended with natural fibres to enhance its properties is called polyester.

Polymer: The compound that are made up of small repeating units, joined together through bonds in a linear pattern is called polymer.

Polythene: The compound obtained from ethylene under high temperature, high pressure and in the presence of a catalyst is called polythene.

Rayon: A man-made fibre which is produced by the chemical processing of wood pulp, which is a natural substance is called rayon.

Synthetic fibres: The fibres which are made by human beings with the help of chemical substances are called synthetic fibres.

Terylene: A common variety of polyester which can be drawn into very fine fibres is called terylene.

Thermoplastics: Those plastics which soften on heating and hardened on cooling are called thermoplastics.

Thermosetting plastics: Those plastics, which when moulded once, cannot be softened again and lose their plasticity are called thermosetting plastics.

On this page, you will find Microorganisms: Friend and Foe Class 8 Notes Science Chapter 2 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 2 Microorganisms: Friend and Foe will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 2 Microorganisms: Friend and Foe

Microorganisms: Friend and Foe Class 8 Notes Understanding the Lesson

1. Microorganisms or microbes are extremely small living organisms which cannot be seen with the naked eyes.

2. Microorganisms can survive under all types of environment.

3. Microorganisms are broadly classified into four categories bacteria, fungi, protozoa and some algae.

4. Viruses are quite different from other microorganisms. They reproduce only inside the host organisms.

5. Some of the microorganisms are beneficial for us, while some are harmful for us.

6. Microorganisms are used in making curd, cake, bread, beverages, etc.

7. Out of several microorganisms contained in curd, the bacterium, Lactobacillus promote the formation of curd.

8. Yeast is a fungi which is used to convert sugar into alcohol. It reproduces rapidly and produces carbon dioxide during respiration.

9. The process of conversion of sugar into alcohol in the absence of oxygen is called fermentation.

10. Microorganisms are also used for producing antibiotics and vaccines. These antibiotics and vaccines stop the growth of other disease-causing microbes.

11. Some bacteria and blue green algae fixes atmospheric nitrogen into the soil. Thus increases soil fertility.

12. Microbes play the chief role in making of manures, which are useful for nourishment of soil.

13. Pathogens are disease-causing microorganisms that can enter our body through the air we breathe, the water we drink, and through direct contact with an infected person or through carriers.

14. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.

15. There are some animals and insects that transfer harmful disease-causing microbes from one body to the other, e.g., flies, mosquitoes, etc., These are called carriers.

16. Anthrax is a harmful human and cattle disease caused by a bacterium.

17. Some microorganisms spoil the food items by producing toxic substances on them. These make the food poisonous causing serious sickness and even death.

18. To save the food from the attack of harmful microbes, some chemicals called preservatives are used. Common preservatives used are common salt, sugar, edible oils, vinegar, sodium benzoate, sodium metabisulphite.

19. Milk is pasteurised for killing harmful microbes. It is heated to about 70° C for 15-30 seconds and then suddenly chilled and stored. This prevents the growth of harmful microbes. This process was given by Louis Pasteur. It is called pasteurisation.

20. Nitrogen Cycle: Some bacteria and blue-green algae present in the soil fix nitrogen gas from the atmosphere and convert it into nitrogenous compounds. These useful nitrogenous compounds are then used by plants from the soil with the help of their roots. They help in the synthesis of proteins and other compounds. On the other hand, there are some bacteria that convert some part of nitrogenous compounds into nitrogen gas again and send them back into the atmosphere.

21. Due to this, nitrogen cycle, the percentage of nitrogen gas in the atmosphere remains more or less constant.

Class 8 Science Chapter 2 Notes Important Terms

Algae: Algae is a vast group of simple, unicellular to multicellular, plant-like organisms which are often present in aquatic habitat, e.g., Chlamydomonas, etc.

Antibiotics: A type of medicine that kills or stops the growth of disease-causing microbes is called as antibiotics.

Antibodies: When harmful pathogens enter our body, our defense mechanism produces substance to fight them, which are called antibodies.

Bacteria: Very small single-celled microbes which have cell walls, but don’t have an organised nucleus and other structures.

Carrier: An animal or insect that transmits pathogens from an infected person to a healthy one is called a carrier.

Communicable diseases: The microbial diseases which can be spread from an infected person to a healthy one through air, water, food or physical contact, etc., are called communicable diseases.

Fermentation: The method in which sugar present in the food is converted into alcohol and carbon dioxide by the microorganisms in absence of oxygen is called fermentation.

Fungi: Fungi are vast groups of microbes which do not have chlorophyll and thus don’t photosynthesise, e.g., yeast, moulds, etc.

Lactobacillus: Bacterium present in curd which promotes its formation.

Microorganisms: Organisms which are too small, to be visible with the naked eyes are called as microorganisms. These include virus, bacteria, fungi, protozoa and a few algae.

Nitrogen cycle: The series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition.

Nitrogen fixation: The process of conversion of atmospheric nitrogen into its usable forms.

Pasteurisation: The process in which the milk is heated to about 70°C for 15 to 30 seconds and then it is chilled suddenly and stored is called pasteurisation.

Pathogens: Pathogens are disease-causing microorganisms.

Preservation: The method used for prevention of spoiling of food by the action of microbes is called food preservation.

Protozoa: Group of single-celled microorganisms, which are also categorised as small animals are called protozoa.

Rhizobium: Bacteria which is present in the root nodules of leguminous plants and fixes atmospheric nitrogen in the soil is called Rhizobium.

Vaccine: Dead or weakened microbes that produces immunity against a disease causing microbe in the living body is termed as vaccine.

Virus: Viruses are microbes which are living only inside another living cell. They are considered intermediate between living and non-living.

Yeast: Yeast are unicellular microbes categorised under fungi are used in fermentation to produce wine, beer and other beverages.